The use of catalysts for the demetallization of hydrocarbons of petroleum origin has been known for some time. Demetallization of such crudes is desirable in order to reduce the concentrations of contaminating metals such as vanadium, nickel, and iron, because the contaminating metals reduce the useful life of contacted catalysts used in refining operations, such as hydrocracking, hydrodesulfurization and catalytic cracking. These contaminating metals act as poisons to the aforesaid contacted catalysts used in refining operations and therefore require that said contacted catalyst be replaced after a shorter period than would otherwise occur.
Various metals have been used as catalysts in eliminating contaminating metals and sulfur present in petroleum hydrocarbons. For example, the elimination of metals can be accomplished by using bauxite as a catalyst, see U.S. Pat. Nos. 2,687,983 and 2,769,758, using iron oxide and alumina, see U.S. Pat. No. 2,771,401, or using macroporous aluminas in a boiling bed, see U.S. Pat. No. 3,901,792.
A multi-step hydrotreatment method overcoming some disadvantages of single step procedures is disclosed in U.S. Pat. No. 3,696,027. This multi-stage process consists of passing a heavy hydrocarbon, at high pressures and temperatures and in the presence of hydrogen, through a three-phase reactor which uses macroporous catalyst particles. This catalyst has a high capacity for accepting metals but a low desulfurizing activity. The effluent as treated by the first macroporous catalyst is then subjected to a fixed-bed reactor phase at a high temperature and pressure together with hydrogen, the fixed bed containing catalyst particles having a moderate desulfurizing activity. Finally, the effluent from the preceding reactor is subjected to a third fixed-bed reactor using high temperatures and pressures, once again with hydrogen, the fixed bed in this phase containing catalyst particles which have a high desulfurization activity.